1. Field of the Invention
The present invention relates to an optometric apparatus for a visual acuity test, and more particularly to an optometric apparatus of table type provided with an internal vision test chart displaying device, and further to a suitable apparatus for confirming a polarized vision chart through a polarizing plate disposed opposite to the examinee's eyes.
2. Description of Related Art
Generally, a vision test chart to be placed at a vision testing distance 5 m from the examinee's eye is used for a visual acuity test, that is, the vision test chart of a direct display type should be disposed actually at a position 5 m apart from the examinee's eyes. However, effectively utilizing the space of a shop is demanded in an optician's shop or the like, therefore, there are known vision testers of reflection display type using reflecting mirrors to display a vision test chart at a virtual vision testing distance, which is shorter than the actual vision testing distance from the examinee's eye.
A vision tester requiring less space was proposed previously by the applicant of the present patent application in Japanese Patent Application No. HEI 3(1991)-144904 contains a vision test chart projector in the operating table, requiring a smaller space. In this vision tester, the optical image projected by the vision test chart projector is reflected repeatedly by plural mirrors contained in the operating table so as to travel toward the outside of the operating table and reflect the optical image toward the examinee's eye by a last mirror disposed in a front of the examinee's eye. More specifically, the mirrors arranged within the operating table comprises plural mirror groups for reflecting the optical image repeatedly to increase the optical distance between the examinee's eyes and the optical image of the vision test chart to the vertical vision testing distance, and a deflecting mirror for reflecting the optical image toward the last mirror disposed in a front of the examinee's eye. After reflected repeatedly by plural mirror groups, the optical image of the vision test chart is reflected by a deflecting mirror toward a last mirror, and traveled to the examinee's eye. By using such vision tester, a space between the optical image of the vision test chart and the examinee's eye is reduced, therefore, the vision testing may be executed in a smaller space.
Another vision tester requiring a smaller space for vision testing has a test chart projector provided in a box (an operating table in the present specification includes the box) placed beside an operating table, reflects the optical image of a vision test chart repeatedly and guides the optical image from the position above the examinee to a mirror disposed opposite to the examinee to reflect the optical image toward the examinee's eye. In this vision tester, the optical path comprises the almost same fundamental construction in a plan view as that of the above mentioned vision tester.
As mentioned above, the latter vision testers needs a smaller space for its establishment than the former providing an operating table separately from a test chart projector.
However, the vision testers comprising plural mirrors need a relatively large table for considerating a space reduced because of reflecting mirror system, and it is difficult to zoom the optical image of a vision test chart for far vision testing and near vision testing selectively in a vision test with a trial lens because a distance between the examinee's eye and a last mirror to reflect the optical image toward the examinee's eye is not enough.
Additionally, when the incident and reflecting plane is changed greatly by reflected through a mirror, the optical image may not disappear even if the polarizing axis of the polarizing vision chart intersects the polarizing axis in the examinee's eye side, thereby some problems may occur in a functional test through the binocular vision, for example that the examinee is unable to find clearly only the optical image for a visual acuity test of one eye, right or left.